Generally speaking, sensors are devices that are responsive to the presence and/or changes in value of a defined variable while sensor systems include functional elements in addition to the sensor that process the sensed variable to provide a utilitarian output. Optical sensor systems include sensors that are responsive to the optical region of the electromagnetic spectrum which broadly includes ultraviolet, visible, and infrared radiation. Optical sensor systems may be designed for various purposes such as detection of electromagnetic radiation, image formation, or image enhancement, and may be designed to be responsive to broad or narrow spectral bands of electromagnetic radiation.
Optical sensor systems such as infrared detectors and the human visual system are responsive to electromagnetic radiation in defined spectral bands, e.g., about 0.7-1.5 .mu.m (near infrared), about 1.5-20 .mu.m (intermediate infrared), about 20-1,000 .mu.m (far infrared), or about 0.4-0.7 .mu.m (visible), respectively. Optical sensor systems are typically configured to be responsive to electromagnetic radiation of certain intensity levels, and may be susceptible to damage or disablement if exposed to electromagnetic radiation of higher intensity levels.
Laser radiation comprises single frequency (or several discrete frequencies), high intensity electromagnetic waves in the optical region of the electromagnetic spectrum. Laser radiation may be encountered in many different environments from the laboratory to the battlefield. There is an increasing tendency to utilize the offensive capability of laser radiation, particularly in hostile environments, to disable or damage optical sensor systems.
Optical sensor systems such as infrared detectors or the human visual system may experience short or long term disablement if intentionally or accidentally subjected to laser irradiation of sufficient intensity levels. Such disabling effects may range from temporary blindness or inoperability of the sensor system to damage sufficient to render the system permanently inoperable.
A need exists to provide protection for optical sensor systems, including the human visual system, from the disabling effects of laser irradiation. While optical filters may provide such protection, optical filters are operative to provide protection only at specific wavelengths or spectral bands. Optical filters may prove satisfactory in the laboratory environment where the wavelength of laser radiation is a known quantity. In the battlefield environment, however, optical sensor systems may be exposed to laser radiation over a wide range of wavelengths. Under such conditions, the efficacy of optical filters may be marginal at best since the wavelengths of laser radiation will be unknown.
Moreover, many optical sensor systems are designed to be responsive to low intensity electromagnetic radiation in defined operating spectral bands. Such optical sensor systems are vulnerable to laser radiation in the operating spectral band(s) of the system. Optical filters cannot be used with such sensor systems since the optical filters would effectively filter out radiation the system was designed to be responsive to. A need exists, therefore, for a protective device for optical sensor systems which is wavelength independent, which prevents laser irradiation in the operating spectral band(s) of optical sensor systems, and which concomitantly allows optical sensor systems to function for their intended purpose within the operating spectral band(s).
In addition, the protective device should provide a field of view that is compatible with the field of view of the sensor system, i.e., the protective device should not reduce the field of view of the sensor system. Furthermore, the protective device should not optically distort the field of view of the sensor system.
The protective device should have a configuration that is compatible with existing as well as nascent sensor systems. The protective device should be configurable as a stand alone unit that may be integrated with existing sensor systems, or configurable as a unit that may be integrally incorporated in the optical train of nascent sensor systems.